The research in this application tests an intergroup emotions theory (JET) approach to understanding prejudice and discrimination against out-groups, and in particular why negative reactions to out-groups are differentiated by situation, context, and occasion. According to JET, social identification with a group triggers intergroup appraisals: interpretations of situations or events according to whether they help or hurt relevant membership groups, rather than the individual self. When appraisals occur at this group level, intergroup emotions are experienced. Such emotions are experienced on behalf of the in-group, and the in-group and out-group become the targets of emotion. Specific intergroup emotions lead to differentiated action tendencies and thus behavior, and also to changes in mental representations. Such differentiated outcomes occur because of and are mediated by specific intergroup emotions that have been triggered by particular appraisals of situations or events related to social identity. Four research projects involving 19 studies focus on key tests of the IET model. Project 1 focuses on the initial process of social identification and on the nature of intergroup emotions. Project 2 focuses on intergroup appraisals and emotions, and particularly the way in which the unique dynamics of intergroup contexts direct such appraisals and emotions. Project 3 is concerned with the consequences of intergroup emotions. Key experiments in this project assess whether intergroup emotions translate into distinct action tendencies and actual behavior, as well as changing the content of mental representations. Project 4 addresses the implications of lET for interventions that undermine or eliminate the negative reactions toward out-groups caused by intergroup emotions. Given the toll that stigmatization and intergroup violence takes on the mental health of individuals and societies, the research is socially relevant as well as theoretically important.